Selective LPCVD tungsten for contact barrier applications.

This study assesses the use of selective LPCVD W as a contact barrier in VLSI circuits. Measurements of the contact resistance and leakage current are evaluated as a function of variations in W deposition parameters, implant type, implant dosage, and metallization heat-treatment. Addition of SiF(4) to alter the equilibrium of the displacement reaction is seen to exhibit minimal erosion and encroachment of the Si contacts as well as produce low and thermally stable contact resistances to both n(+) and p(+) diffusions. For surface doping concentrations of 2.45 x 10(20) cm(-3) As and 0.62 x 10(20) cm(-3) B, measured values of contact resistance for 2.0microns-sized vias are near 20 and 30 omega respectively. These values are indeed quite compatible with high performance CMOS device requirements. Further reductions in values of contact resistance are achieved with use of a self-aligned PtSi/W contact barrier metallization. For typical surface doping concentrations of 1.44 x 10(20) cm(-3) As and 0.62 x 10(20) cm(-3) B, measured values of contact resistance for 2.0micron-sized vias are in this case near 4 and 15 omega respectively. Sporadic leakage across shallow n(+)/P-Tub junctions remains, however, a serious problem associated with this selective LPCVD W process. Understanding the origin of this leakage and eliminating it can lead to numerous applications of this technology in VLSI manufacturing.